As semiconductor fabrication moves toward maximizing circuit density, electrical components are formed at a number of layers and different locations. This requires electrical connection between metal layers or other conductive layers at different elevations in the substrate. Such interconnections are typically provided by forming a contact opening through insulating layer to the underlying conductive feature. With increasing circuit density, the dimensions of openings for electrical contacts become narrower and deeper, posing a challenge to provide adequate conductive fill within high aspect ratio openings.
Typically, in forming a contact plug, a thin layer of titanium is deposited over the top of a silicon base layer (substrate), and tungsten or other electrically conductive plug material is then deposited from tungsten hexafluoride (WF6) by chemical vapor deposition (CVD) to fill the contact hole. However, there are several limitations of tungsten (W) plugs. Tungsten does not provide an adequate fill for high aspect ratio features. In addition, the use of WF6 as a precursor gas in the formation of tungsten plugs, can result in the penetration of the fluoride component into the adjacent dielectric layer causing lateral encroachment and wormholes.
Titanium nitride (TiN) films have attractive properties that may overcome the limitations of tungsten plugs as integrated circuit (IC) devices continue to shrink below 0.15 micron dimension. TiN films have been deposited by low pressure chemical vapor deposition (LPCVD) using tetrakisdimethylamidotitanium (TDMAT) and ammonia as precursor gases. However, TDMAT films have a high carbon content and when subjected to high temperatures in the presence of oxygen, become porous and, therefore, are unusable as a conductive contact.
Thin TiN films and liners have also been deposited from titanium tetrachloride (TiCl4) and ammonia (NH3) by CVD onto a titanium (Ti) liner overlying the insulative layer. Although useful for forming a thin liner, when pure TiCl4-based TiN is deposited to fill a via or other contact opening, the material does not adhere well to the Ti thin layer, particularly when the TiN layer becomes greater than about 150 to about 200 angstroms thick.
In addition, it has been found that chlorine (Cl2) within a contact fill material such as TiN, which has been deposited from a chlorine-containing precursor such as TiCl4, can diffuse into and corrode an overlying interconnect (e.g., aluminum), thus ruining the device.
Another problem lies in the formation of a conductive contact (e.g., contact plug) in a contact hole or via. Typically, a conductive material is blanket deposited over the surface of the substrate including into the contact hole, thus forming a continuous film. If an anneal is needed, the continuous film layer is typically subjected to a high temperature anneal, and then excess material is removed from the surface of the substrate by a chemical mechanical polishing (CMP) process, leaving the contact plug within the hole. A problem arises, however, during the high temperature anneal with cracking of the blanket material layer.
Therefore, it would be desirable to provide a conductive contact and a method of forming the contact that avoids such problems.